The primary objective of these investigations is to study the metabolism of hnRNP and mRNP, the relationship between them, and the conversion of inactive cytoplasmic mRNP into translatable polysomal mRNP during the development of the cryptobiotic gastrulae of the brine shrimp Artemia salina. Events in protein synthesis on resumption of development of A. salina embryos are strikingly similar to those in newly fertilized eggs. We plan to continue the identification, purification and characterization of RNA binding proteins involved in the packaging and regulation of expression of mRNA. We will attempt to develop an in vitro system to investigate the biosynthesis of mRNP. We will continue investigations on the specific role of protein HD40 (a RNA helix-destabilizing protein, MW 40,000, was purified to homogeneity from undeveloped embryos), a major component of MRNP. Nuclei of developed embryos also contain HD40 and several antigenically related proteins. We will develop a new method of isolation of mRNP and, possibly, hnRNP using antibodies to HD40 immobilized on a solid support. We have recently shown that HD40, which is very similar in amino acid composition and molecular weight to major hnRNP proteins from mammalian cells, forms a ribonucleoprotein complex having a "beads-on-a-string" structure with properties similar to those of the hnRNP complex. The progressive unfolding of the polynucleotide by HD40 is followed by the formation of regularly spaced globular structures along the polynucleotide chain. We will further characterize the interaction of HD40 with RNA and we will investigate the possibility that cytoplasmic mRNP and hnRNP share some common structural features. We intend to extend these studies into selected mammalian and plant cells to find out whether HD40 represent a new class of RNA binding proteins.